The present invention relates to a photomultiplier tube segmented into a plurality of elementary photomultipliers, comprising a photocathode, a plurality of elementary electron multipliers of the "apertured sheet" type, and a plurality of focusing electrodes providing the convergence of the photoelectrons emitted by the photocathode towards the elementary multipliers.
The invention is particularly suitable for use in the field of high energy physics, and, more specifically, in the field of the detection by photoelectric effects of elementary particles so as to determine, for example, the trajectory. To this effect, it is necessary to provide detection arrangements comprising a large number of separate photomultipliers elements but which are joined to the best possible extent so as to limit the loss of useful surfaces of these arrangements. A solution of this general technical problem which at the same time has the advantage that it reduces the cost of the said detection arrangements, is obtained by dividing a photomultiplier tube into a plurality of elementary photomultipliers. The European Patent Application no. 0 264 992, which corresponds to U.S. Pat. No. 4,816,718, describes a segmented photomultiplier tube of a type as defined in the opening paragraph, in which the elementary multipliers are obtained by partitioning a single "apertured sheet" multiplier, the input space of which situated between the photocathode and the electron multiplier is also partitioned, in such a manner that it is impervious to the electrons emitted by the photocathode, into a plurality of elementary input spaces. This partitioning of the input space base for its effect that crosstalk of photoelectrons which might occur between the different parts is prevented because of the fact that the distance between the photocathode and the multiplier must be relatively large to enable antimony generators, for example, to be positioned sufficiently remote from the input window of the tube for applying during the manufacture of the photocathode, an antimony layer which is as uniform as possible and, also, that the focusing electrodes are raised to a a high electric potential, of the order of the potential of the first sheet of the electron multiplier.
Furthermore, it should be noted that the partitioned multiplier of the prior-art segmented photomultiplier tube is not free from crosstalk. When, for example, the European Patent Application no. 0 350 111 is examined, which describers a "sheet" multiplier of the same type as that used in the prior-art segment tube, it will be seen that the partitioning is made between the extracting and multiplying half-dynodes of the same dynodes of the same dynode with the aid of a brace which is impervious to electrons. In contrast thereto, the space between a multiplying half-dynode and the extracting half-dynode of the subsequent dynode is free, so that electrons which are elastically back scattered to the surface of the said extracting half-dynode near the boundary between two elementary multipliers can pass from an elementary multiplier to the adjacent elementary multiplier to be multiplied there again and, thus, cause crosstalk.